Someone can correct me if I'm wrong, but .85 of a mb is too slow of a speed to get HQ to run smoothly on the ipad, thus the stopping and starting of the stream. That's the same speed I'm getting from my slingbox right now. Picture quality is fine for me on the slingcatcher and on the PC, but on the iphone, SQ is all I can get out of the app. When I change to HQ, the same stopping and starting you're getting also happens to me.
If the information you posted is right, the connection speed is not good enough for the Slingbox PRO HD. Make sure to check this link in order to get the tech specs for the Slingbox PRO HD.